Braking systems are employed in many areas of technology, including motor vehicles and various types of machinery. Friction brakes such as drum brakes or disc brakes are commonly used for slowing and stopping rotating shafts in vehicles and machinery. However, there are several disadvantages associated with friction braking. A particular disadvantage is the wear on the brake pads or shoes and discs, which are brought into contact to slow the rotary motion of the shaft by friction. A further disadvantage is the generation of heat by friction and also the need to remove that heat to avoid deformation.
Several other types of braking systems are also known. One type of braking system which does not rely on friction is a liquid resistance brake. This type of brake may be based on one or more gear pumps. A simple gear pump 100 is shown in FIG. 1 of the accompanying drawings. The gear pump comprises a driver gear 102 and an idle gear 104 arranged in a housing 101. Rotation of driver gear 102 by shaft 103 causes gear 104 to rotate. As the gears 102, 104 rotate they separate on the inlet side 105 of the pump 100. This creates an area of lower pressure on the inlet side 105, thereby drawing 25 fluid into the pump. The fluid is carried by the gears 102, 104 (in small volumes 107) to the outlet side 106, where the meshing of the gears displaces the fluid. Typically, the mechanical clearances in gear pumps are small to prevent the fluid from leaking backwards.
Liquid resistance brakes use the basic principle of a gear pump but with the inlet and outlet connected together through a valve. While the valve remains open, the shaft can freely turn, pumping fluid around the system. Once the valve is closed, the fluid pressure increases and restricts rotation of the gears and thus of the shaft.
Due to their non-friction operation, liquid resistance brakes are particularly suitable in applications where the maintenance costs of replacing worn brake pads are high or where heavy and constant wear makes brake pads too expensive to operate (such as in large sized vehicles like mining trucks). The non-friction operation is also of use in applications where heat generation or material distortion is a problem (such as in micro braking applications or explosive environments). Liquid resistance brakes are also suitable for regenerative braking applications where the excess energy generated during braking can be captured and reapplied to an alternative task (such as in regenerative braking systems used in light rail systems and next generation Formula One cars).
An example of this type of brake is described in U.S. Pat. No. 5,558,187. The apparatus comprises a fluid-tight housing in which is disposed a shaft rotational engagement gear having an exteriorly-accessible portion thereof rotatably engageable with a shaft. A plurality of compartments is formed with the housing and the compartments are in fluid communication with each other through openable and closable valves. The housing is substantially filled with a fluid which is flowable through the valves in direct relation to the openness of the valves. The apparatus further comprises a plurality of compartment-divider gears rotatably engaged with the shaft rotational gear and situated in cooperation with the compartment walls to create restriction seals between the compartments. When the valves are closed, the flow of fluid between the compartments is retarded and the fluid pressure is increased. The increased fluid pressure slows the gears which in turn slow the rotating shaft engaged with the rotational engagement gear, simultaneously decreasing fluid pressure.
A disadvantage of this system is that the brake will always be substantially larger in diameter than the shaft, resulting in an additional space requirement and an additional cost in terms of components.
It is desirable to provide a liquid resistance braking system which provides improved performance over known brakes of this type.